Sadly, it's much easier to create a desert than a forest.

The tropical rain forests are a telling example. Once cut down, they rarely recover. Rainfall drops, deserts spread, the climate warms.

One thing that being a scientist has taught me is that you can never be certain about anything. You never know the truth. You can only approach it and hope to get a bit nearer to it each time. You iterate towards the truth. You don't know it.

The climate is doing its usual tricks. There's nothing much really happening yet. We were supposed to be halfway toward a frying world now.

Our future is like that of the passengers on a small pleasure boat sailing quietly above the Niagara Falls, not knowing that the engines are about to fail.

The problem is we don't know what the climate is doing. We thought we knew 20 years ago. That led to some alarmist books - mine included - because it looked clear-cut, but it hasn't happened.

Geological change usually takes thousands of years to happen but we are seeing the climate changing not just in our lifetimes but also year by year.